In a typical flip chip thermocompression bonding process, a flip chip is held on a bond collet of the bond head of a flip chip bonder by a vacuum suction force. Accordingly, flip chips can be individually transferred from a supply of flip chips to a substrate for thermocompression bonding. After a flip chip is held on the bond collet, an imaging system is used to determine the flip chip position in relation to a desired substrate location for bonding thereto. Specifically, the imaging system includes an uplook pattern recognition system to determine the flip chip position. The uplook pattern recognition system may either be a fixed or moving uplook camera. The imaging system also includes a downlook pattern recognition system to identify the desired substrate location to which the flip chip is to be bonded. The downlook pattern recognition system is typically a moving downlook camera for locating a desired bond pad position of the substrate. Based on the data captured by the imaging system, the bond head of the flip chip bonder will accordingly move horizontally along the X axis and/or the Y axis, and/or rotate about a vertical Z axis by an angle of theta, in order to reposition the bond collet so that the flip chip will be accurately placed on the substrate. Thereafter, the bond collet will be moved vertically downwards along the vertical Z axis at a Z-axis speed towards the desired bond pad position of the substrate until the flip chip contacts with the desired bond pad position and thermocompression bonding is then carried out. The process cycle repeats for a next flip chip that is picked up by the bond collet, with each process cycle typically requiring about 3.5 seconds. Accordingly, the throughput capacity of the conventional flip chip bonder in terms of units-per-hour (UPH) is about 500. The flip chip thermocompression bonding process also involves adhering to various profiles such as a bond force profile between the flip chip and the substrate, a temperature profile of the bond collet, and a position profile of the bond collet.
Due to the transfer of flip chips individually to the substrate, the throughput capacity of the flip chip bonder for performing thermocompression bonding is limited. This is exacerbated by various operating considerations, such as the need for precise alignment between the flip chips and the corresponding bond pad positions of the substrate to which the flip chips are bonded, a slow Z-axis speed required to avoid formation of air voids in the adhesives dispensed on the substrate bond pads upon contact with the flip chips, a low temperature required for the contact between the adhesives and the flip chips which increases curing time, a long heating time to heat up the flip chips which increases the duration of each cycle of the thermocompression bonding process, and a long cooling time to cool the bond collet before a next flip chip is picked up.
Thus, it is an object of this invention to ameliorate the limitation of conventional flip chip bonders for thermocompression bonding, and to provide the general public with one or more useful choices.